Automatic repetitive registration and image wise exposure of sheet substrates

ABSTRACT

Method and apparatus for registering and imagewise exposing to actinic radiation a sequence of similar sheet substrates. A liquid layer separates the photosensitive layer and each photomask during the exposure step.

BACKGROUND OF THE INVENTION

There is a continuing need in the printed circuit, graphic arts, andrelated industries to transfer images photographically from original(positive or negative) photomasks to one or both sides of a lightsensitive sheet element in a repetitive manner. In many important cases,these images must be aligned or registered precisely to locationspreviously established on the element. In the case where images aretransferred to both sides of the element, it is often further requiredthat the front and rear images also be registered precisely to eachother. In all cases, the photographic operation is carried out in amanner which maintains, to the greatest precision possible, both thedefinition and the relative locations of the features of the images,while minimizing the transfer of undesired or spurious features.

Printed circuits are often prepared by a repetitive image transferprocess using dry film photoresists. The equipment used to practice thephotoresist process has consisted in general of discrete pieces such asa cleaner or scrubber for cleaning the copper-clad substrate boards, anoven for preheating the boards, a roll laminator applying heat to thefilm and board as it laminates them together, an actinic radiationexposure station, and solvent wash-out apparatus for developing a resistimage on the copper substrate. Such processes and equipment are fullydescribed in Coombs, "Printed Circuits Handbook", McGraw-Hill SecondEdition (1979) and in DeForest, "Photoresist Materials and Processes",McGraw-Hill (1975).

Typically, manual transfer and positioning of the substrate board occursbetween each piece of equipment which increases expense and lessensreproducibility, leading to yield loss in the process.

Various attempts have been made to automate the photoresist process butautomation has been adopted to only a limited extent. Recently, however,board trimming has been successfully incorporated into an integratedhigh productivity cleaning and laminating system as disclosed in U.S.Pat. No. 4,293,635 and European Patent Application No. 81104013.8, U.S.Ser. No. 153,636, abandoned and U.S. Ser. No. 153,637, abandoned, bothfiled May 27, 1980. This automation results in substantial cost savingsto the user. Nevertheless, many of the subsequent steps remain highlylabor intensive and prone to human error. This is particularly true ofthe registration and exposure steps.

Contact printing is virtually the universal method of exposure usedtoday in printed circuit photofabrication despite certain knownshortcomings. Although low in equipment costs, simple to use, andcapable of excellent line definition, contact printing is laborintensive and slow (because of long vacuum draw-down times). It also issubject to losses due to damaged or dirty photomasks resulting fromrepeated use. This, in turn, requires frequent and expensive touch upand replacement of photomasks to avoid yield penalties. Much time isalso lost in the constant and tedious process of inspecting photomasksfor defects between exposure. In addition, variations in frametemperature and ambient humidity affect corner-to-corner registration,especially for large boards, unless expensive, fragile, glass photomasksare used.

Alternative exposure methods such as gap printing, projection printingand laser scanning each offer some significant advantages over contactprinting. However, in the current state of development, all have seriouslimitations for high productivity applications and are intrinsicallymuch higher in equipment cost.

SUMMARY OF THE INVENTION

The present invention is directed to a process of registering andimagewise exposing to actinic radiation a sequence of similar sheetsubstrates, each substrate containing a photosensitive layer, comprisingthe steps of:

(1) advancing a substrate to a position in a device to undertake ineither order or concurrently

(a) aligning the substrate and a photomask in a predeterminedrelationship to one another,

(b) applying a liquid between the photosensitive layer and thephotomask,

(2) contacting through the liquid layer the substrate containing thephotosensitive layer and the photomask whereby during said contactingsubstantially no movement of the photosensitive layer relative to thephotomask occurs other than a more intimate contact due to displacementof the liquid in a liquid layer and whereby at least one of interfacialor viscous force due to the liquid layer aids in holding thephotosensitive layer and photomask in a fixed position relative to oneanother;

(3) exposing the photosensitive layer to actinic radiation through thephotomask;

(4) removing the photomask from the exposed photosensitive layer;

(5) removing the substrate from the device whereby steps 1 to 5 can berepeated; and

(6) repeating steps 1 to 5 for each of said similar sheet substrateswhereby substantially identical imaged substrates are obtained.

In a preferred embodiment of the process of the present invention, bothsides of the substrate contain photosensitive layers and both layers areexposed to actinic radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription thereof taken in connection with the accompanying drawings,which form a part of this application and in which:

FIGS. 1 and 2 are, respectively, a front and side elevation of a circuitboard exposure apparatus in accordance with the present invention;

FIG. 3 is a perspective view of a photomask carrier assembly used in thecircuit board exposure apparatus of the present invention;

FIGS. 4A and 4B together illustrate a plan view of a board registrationand of a board clamping arrangement used in a circuit board exposureapparatus of the present invention taken along view lines 4--4 in FIG.1;

FIGS. 5A and 5B together illustrate a front elevation view of theelements shown in FIGS. 4A and 4B, respectively, and further provide afront elevation view of one roll used in the laminating arrangement ofthe circuit board exposure apparatus of the present invention;

FIGS. 6 and 7 are side elevation views partially in section taken alongsection lines 6--6 and 7--7 respectively in FIG. 4A illustrating theregistration arrangement of the circuit board exposure apparatus in theopen and closed positions;

FIG. 8 is front elevation view partially in section taken along sectionlines 8--8 in FIG. 4A;

FIG. 9 is a plan view taken along section lines 9--9 in FIG. 1illustrating the laminating arrangement used in the circuit boardexposure apparatus of the present invention;

FIG. 10 is an elevation view partially in section taken along sectionlines 10--10 in FIG. 9;

FIG. 11 is a side elevation view similar to FIG. 7 illustrating theapplicator arrangement used in the circuit board exposure apparatus ofthe present invention;

FIG. 12 is a side elevation view of a photomask take-up roll used in thecircuit board exposure apparatus of the present invention;

FIG. 13A to 13C taken together illustrate a front elevation view of aboard conveyor arrangement used in the circuit board exposure apparatusof the present invention, while FIGS. 13D and 13E are section viewsthrough the lower and upper conveyor belts, respectively;

FIG. 14 is a side elevation view of the board conveyor arrangement shownin FIGS. 13A to 13C;

FIG. 15 is a front elevation view of a board transfer arrangement usedin the circuit board exposure apparatus of the present invention;

FIGS. 16A and 16B are side elevation views of the board transferarrangement shown in FIG. 15 in the board receive and board depositpositions, respectively; and

FIG. 17 is a stylized schematic representation of the circuit boardexposure apparatus of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the process of this invention a sequence of substrates containing aphotosensitive layer with or without a top support sheet is introducedin sequence into a registration and exposure device. This substrate withthe photosensitive layer which may have a separate top support film isalso referred in the present disclosure as a sensitized substrate and asa circuit board. The photosensitive layer composition which is notpresent as a liquid preferably comprises a photosensitive polymer whichcan be negative or positive working. Conventionally the substrate isrectangular. The registration portion of the apparatus consists of oneor two film elements, preferably rectangular and flexible, at least oneof which is a photomask. The leading edges of the elements can be joinedin parallel, hinged, relationship on each side of a thin rectangularcarrier whose thickness approximates the thickness of the photosensitivesheet. The hinged relationship maintains the registration between thephotomasks and the carrier. When both film elements are photomasks, theyare maintained in precise register with each other by virtue of theirhinged relationship to a common carrier.

With the photomasks hinged outward from the carrier, the sensitizedsubstrate is positioned or aligned between the film elements so that onesubstrate edge is in registration contact and approximately parallel tothe length of the carrier. In some instances registration contact can besimple edge-to-edge contact of the substrate with the carrier whereinthe only added criterion is that the image pattern portion of thephotomask is completely contained within the area of the sheet to beimaged. However, registration contact more generally requires theprecise alignment of details contained on the photosensitive sheet ofthe substrate with details of the photomask image or images. In thisinstance at least two contact points on or in the sheet are brought intoa fixed relationship with two corresponding contact points fixed to thecarrier. Such points may be notches and tabs suitably spaced on thesheet and carrier edges. Alternatively the points may consist ofregistration pin and hole combinations wherein the sheet containsprecision drilled registration holes which are positioned in the desiredorientation to the bar by registration pins. The registration issubstantially identical from substrate to substrate to obtain a seriesof substantially identical exposed photosensitive layers on thesubstrates for subsequent processing.

Once the sensitized substrate is in registration relationship to thecarrier, the flexible film photomasks can be applied to opposite sidesof the sensitized substrate in the presence of a liquid interface byapplying normal pressure in a line roughly parallel to the carrier onthe outer surfaces of the photomasks at or near the hinged edges andadvancing (relatively) the pressure line in the direction perpendicularto the hinge line and parallel to the sensitized substrate surface and,concurrent with the advance, applying the liquid, e.g., by spraying, tothe nip between the substrate and the inner surface of the photomaskformed by the advancing pressure line. In effect the photomasks aretemporarily wet laminated to both sides of the sensitized substrate togive a registered sandwich structure in which the sensitized substrateis separated from each photomask surface by a liquid interface. Thislamination process step is preferably carried out by passing the hingedphotomask-registered sheet assembly through a pair of pressure rollers.In this mode of operation, pressure is applied at or near the hingedleading edge of the sensitized substrate and the flexible photomasks andthe trailing portions of each photomask wrap partially around the curvedsurface of each pressure roll. Liquid, preferably water, is then sprayedinto the two nips on each side of the sensitized substrate. Preferably,the registration apparatus is oriented so that the general direction ofthe wet lamination is upward, i.e., the sensitized substrates travels inan upward direction relative to the pressure rolls and liquidapplicators. When so oriented, a cleaning action of the liquid can beachieved on both the photomask and the photosensitive layer or supportsheet which is enhanced by the use of excess liquid directed at bothsurfaces and which will simply drain into a catching basin carrying anyextraneous matter with it. In addition, the area above the pressurerolls where actinic exposure preferably occurs can more easily be keptfree of unwanted liquid. This process of obtaining alignment of asubstrate and photomask is obtained without the use of vacuum. Althougha suction can be used to remove excess liquid, it is understood that avacuum is not necessary for holding the substrate and photomask incontact with one another.

It is understood that in the present specification during the liquidcontact of the substrate and photomask "substantially no movement" meansthat surface of the photosensitive layer and the photomask do not moverelative to one another in directions parallel to their surfaces, i.e.,the surfaces do not slide relative to one another to change thealignment of the photomask to the substrate. However, it is understoodthat "substantially no movement" allows relative movement of thephotomask and the photosensitive layer in the direction perpendicular totheir surfaces to form a more intimate contact, e.g., as liquid issqueezed from the interface between the photosensitive layer and thephotomask. However, the photosensitive layer and photomask, alreadycontacted by the advancing pressure line, will remain in a fixedrelationship in directions parallel to their surfaces.

Also it is understood in the present specification that "contacting"through the liquid a substrate containing a photosensitive layer and aphotomask does not exclude intermediate layers. For example thephotosensitive layer may have a support or cover sheet which allowsactinic radiation to pass or the photomask may contain a releasecoating. Such support or cover sheet or release coating could contactthe liquid.

In the present specification a photosensitive layer is employed to meana preformed layer and excludes a photosensitive layer present as aliquid.

Once the photomasks have been fixed in register over the photosensitivelayer, the substrate with its photosensitive material may be exposed toany source of radiation actinic to the photosensitive material for aprescribed period of time. In a preferred mode of operation, thelaminated element emerges from the pressure rollers, is stopped andsuspended in a fixed upright position and uniformly exposed to actinicradiation in the 3000 to 4000 Å or above region. When both sides of thesubstrate are photosensitive, both sides preferably are exposedsimultaneously. In an alternative mode of operation, the sensitizedsubstrate is irradiated with actinic radiation as it emerges from thepressure rolls and is carried past the irradiation region. In this mode,the irradiation may be focused to a band or a transversely scanned spotof intense actinic radiation may be used which can be modulated to matchthe image to be recorded to the exposure characteristics of thephotosensitive surface and the rate of transport. It is also possible tocompletely remove the sensitized substrate from the registration deviceand expose it on any suitable exposure unit. In this instance thephotomasks and carrier remain fixed in registration with thephotosensitive layer by the action of surface or viscous forces inducedby the interface liquid and no separate device, e.g., a vacuum force, isneeded to maintain intimate contact. It is understood that both surfaceand viscous forces may be present.

In the above process steps the rectangular, flexible film elements havebeen identified as photomasks. When both sides of an element to beimaged are photosensitive, as with two sided circuit boards, both filmelements contain opaque and transparent image areas. However, when onlyone side of a photosensitive element is to be imaged, e.g., a one-sidedcircuit board, only one film element (of a pair, if present) is requiredto be a photomask.

When imaging exposure is complete, both photomasks are peeled from thesurfaces of the exposed photosensitive element thus releasing the imagedelement from registration. The imaged element is then transferred fromthe registration-exposure apparatus to a subsequent processing station,e.g., solvent development. The hinged photomask-carrier assembly isreturned to its initial position to receive the next sensitizedsubstrate and repeat the registration-exposure sequence. In a preferredmode of operation, after exposure, the pre-exposure process steps, forthe most part, are reversed. Thus the exposed laminated element passesback through the pressure means such as rollers and each photomask ispulled back over its respective pressure roller into a storage areauntil the hinged area on the carrier is reached. Other means thanrollers may be used to apply pressure, e.g., a squeegee. At or near thispoint the photomask-carrier assembly stops and the imaged substrate isejected to a device which conveys the substrate from theregistration-exposure apparatus. Also, the pressure means may be movableand the apparatus holding the registered substrate with the photomaskmay be stationary. In such a mode of operation the apparatus would besubstantially ready to accept the next sheet in the series to beexposed. In the preferred operation after exposure, the motion of theimaged substrate is in a downward direction and the pressure rollers areseparated to allow the imaged substrate to drop to the conveying means.The photomasks can be stored in any number of ways as they are peeledfrom the imaged sheet. The preferred mode of storage is on a take-updrum on which the photomask surface remains free of extraneous contact.Alternatively, the photomasks can be stored suspended, or can be woundaround the pressure roller itself.

The sheet substrate during the registration and imagewise exposureprocess may be in any orientation including a horizontal plane orvertical plane. Also the substrate may move in a relative downwarddirection. Preferably the substrate will be in a vertical orsubstantially vertical plane and which move in a relative upwarddirection. In the process of this invention any means can be used toconvey the sensitized substrate to and from the registration position inthe apparatus. For the preferred mode of operation in an upward-downwarddirection, the sensitized substrate can be conveyed horizontally on itsedge by a belt until positioned under the carrier at which point it iselevated into registration contact by a lifting device. After exposure,the imaged sheet is dropped to the conveyor belt which conveys ithorizontally on edge out of the apparatus.

The liquid which is applied to the photosensitive layer or support sheetand photomask serves several vital functions in the process of thisinvention. The liquid serves to uniformly fix the photomask in intimateregistered contact to the photosensitive surface or support sheet duringactinic exposure and after exposure allows the photomask to be easilyremoved from the exposed sensitized substrate without damage or transferof either. Preferably a large excess of liquid is flushed over thesurfaces of both the phototool and substrate. The excess liquid servesto clean repeatedly the surface of the photomasks and individually eachphotosensitive surface or support layer thus preventing buildup ofelement born dirt with subsequent deterioration of the photomask imageand/or the resulting exposed image. Besides these vital functions theliquid also serves to condition and cool the photomask which tends toget warm as it absorbs radiation during the repeated exposures. Thus,during repeated exposure, the environment and temperature of thephotomask is maintained constant and less susceptible to changes inambient temperature or humidity. In this respect, it is also desirableto spray liquid on the exterior surface of the photomask, provided theliquid forms a uniform film on the exterior surface or is removedtherefrom before actinic exposure. The liquid interface should besubstantially transparent to actinic radiation and should not damage thephotomask or the photosensitive sheet surfaces or cover sheet. Also itshould not interfere with the exposure of the photosensitive layer. Theliquid should preferably wet both surfaces of the photomask andphotosensitive layer of support sheet, have low volatility at ambienttemperatures, and have sufficient viscosity to fulfill the vitalfunctions of the liquid. The preferred liquid is water or aqueoussolutions containing adjuvants which improve liquid characteristics,e.g., surface active agents, viscosity adjusting agents, etc. Otherliquids, of course, can be used depending on the conditions required,e.g., alcohols, glycols, glycol ethers, halogenated hydrocarbons,paraffins, etc., provided they fillfil the above criteria. In aninstance when long exposure times are required with actinic sourceswhich induce buildup of heat, a high boiling point liquid like ethyleneglycol is preferred. Since the liquid remains a liquid after theexposure step, a photosensitive liquid is not used for this component ofthe process.

The repetitive process of this invention is particularly suited to themass production of identical circuit boards. In addition the process isuseful in many image reproduction processes where multiple copies orimages are needed. Thus identical lithographic printing plates,photomask transparencies, multicolored pictures, etc. are possible bythe process of this invention using the technology disclosed for examplein U.S. Pat. Nos. 3,060,024; 3,458,311; 3,582,327; 3,649,268; 4,053,313;4,054,483; 4,126,466; 4,157,407; 4,173,673; 4,174,216; 4,191,572; and4,323,637 which are incorporated herein by reference.

The process of this invention is useful for imaging any sensitizedsubstrates which is compatible with the liquid treatment. If thephotosensitive composition is not compatible with the liquid preferablya support or cover sheet than will be used to protect the composition.In such a case the support sheet will contact the liquid. The process isparticularly useful for exposing elements having a photoresist surfaceor surfaces which are typically used for producing printed circuitboards, lithographic printing plates or any other thin mask image.

The repetitive registration and imagewise exposure process of thepresent invention is applicable to a wide variety of sheet substratesprovided at least one surface contains a photosensitive layer with theoptional support sheet. In a preferred mode, opposite surfaces of thesheet substrates carry photosensitive layers with the registration andimagewise exposure performed simultaneously or substantiallysimultaneously on both surfaces.

In one of the modes of the invention, the sheet substrate will contain asmooth surface, e.g., copper, onto which the photosensitive layer islaminated. In such case, the substrate surface over which thephotosensitive polymer layer is laminated will be free of circuitry(although through-holes may be present).

Alternatively, the substrate surface onto which the photosensitive layeris laminated may contain circuitry in relief and need not be smooth. Insuch case, the registration and imagewise exposure process can takeplace in similar fashion to a smooth surface, including simultaneous orsubstantially simultaneously registration and imagewise exposure ofopposite surfaces which have photosensitive polymer layers.

In practicing the invention, a sheet substrate bearing photosensitivefilm resists of various types, e.g., negative and positive working, maybe used. In general photohardenable, negative-working resists can bephotopolymerizable films of the type disclosed in U.S. Pat. No.3,469,982 and the photocrosslinkable elements of the type disclosed inU.S. Pat. No. 3,526,504. Positive-working, resist elements may be of thephotosolubilizable type, e.g., suh as the o-quinone diazide elements ofU.S. Pat. No. 3,837,860, or of the photodesensitizable type, e.g., suchas the bisdiazonium salts of U.S. Pat. No. 3,778,270 or thenitroaromatic composition disclosed in U.S. Pat. No. 4,269,933 or U.S.Pat. No. 4,162,162.

The photosensitive layer used in the process is preferably processiblein aqueous alkali in the sense that it is soluble and therebydevelopable in an aqueous alkali solution, e.g., 1 wt. % Na₂ CO₃ at29.4° C. when sprayed for 90 seconds.

An element containing an image-yielding, nonblocking photopolymerizablestratum on a strippable support is preferably used such as the onedescribed in copending U.S. Pat. No. 4,293,635 and applied to asubstrate by the processes described in EP08110413.8 and U.S. patentapplication Ser. No. 153,636 filed May 27, 1980, abandoned.Alternatively, particularly if the photopolymerizable layer is tacky,the remaining surface of the supported, photopolymerizable stratum maybe protected by a removable cover sheet and is applied to a substrate bythe process described in U.S. Pat. No. 3,469,982. The photosensitivecomposition is preferably about 0.0003 inch (0.0008 cm) to about 0.01inch (0.025 cm) or more thick. The photosensitive element may be rigidor highly flexible depending on the desired end use of the processedelement. Also, in instances where the photosensitive layer isself-supporting, e.g., such as elements disclosed in U.S. Pat. No.4,054,479, an underlying substrate portion which is not photosensitivewould be present.

The substrate supporting the photosensitive layer may be any sheetmaterial which is compatible with the end use of the layer and includemetal foils or plates, metal clad boards, plastic films, sheets orplates, glass or ceramic plates, impregnated fiber boards or paper,foraminous sheet material like paper, cloth, or screens. The substratesurface may be planar or may contain a relief image or pattern of eitherthe same or a different material, e.g., a printed circuit. In apreferred process of this invention, the substrate contributes to theproduction of a printed circuit.

Generally, suitable substrates for the process of the inventioninvolving printed circuit formation are those which have mechanicalstrength, chemical resistance and good dielectric properties. Thus, mostboard materials for printed circuits are thermosetting or thermoplasticresins usually combined with a reinforcing agent. Thermosetting resinswith reinforcing fillers are ordinarily used for rigid boards, whereasthermoplastic resin without reinforcements are usually used for flexiblecircuit boards. Ceramic and dielectric coated metals are also useful.

Typical board construction involves combinations such as phenolic orepoxy resins on paper or a paper-glass composite, as well as polyester,epoxy, polyimide, polytetrafluoroethylene, or polystyrene on glass. Inmost instances, the board is clad with a thin layer of electroconductivemetal of which copper is by far the most common. Frequently the boardswill contain holes for component mounting, for interconnecting circuitlayers, and for registration.

It is essential that the printed circuit substrates used in the processof the invention be clean and free of any extraneous materials to insurethat these materials do not interfere with wetting and bonding of thesurface. For this reason, it will frequently be desired to clean printedcircuit substrates prior to lamination of the dry resist film by one ormore of the several cleaning processes which are well-known in the fieldof printed circuit board manufacture. The particular type by cleaningdepends upon the type of contamination, e.g., organic, particulate ormetallic. Such methods include degreasing with solvents and solventemulsions, mechanical scrubbing, alkaline soaks, acidification and thelike, followed by rinsing and drying. A particularly preferred processof substrate cleaning and resist application to form a sensitizedsubstrate is disclosed in U.S. patent application Ser. No. 153,636,filed May 27, 1980 refiled as Ser. No. 341,618, No. 4,405,394.

Suitable substrates for the process of the invention involvingpreparation of lithographic printing plates are those which havemechanical strength and surfaces which differ in hydrophilicity oroleophilicity from the surfaces of the imaged photosensitive areaslaminated thereto. Such substrates are disclosed in U.S. Pat. No.4,072,527. While numerous substrates are satisfactory for this purposethin anodized aluminum plates such as disclosed in U.S. Pat. No.3,458,311 are particularly useful.

A suitable substrate material for preparing a mask image is atransparent polymeric or glass sheet or plate with suitable subcoatingsor surface treatment if needed. Polymeric sheets preferably have a highdegree of dimensional stability to temperature changes, may be chosenfrom a wide variety of films composed of high polymers, e.g.,polyamides, polyolefins, polyesters, vinyl polymers, and celluloseesters, and may have a thickness of from 0.0002 inch (0.0006 cm) to0.008 inch (0.02 cm) or more. A particularly suitable substrate is atransparent polyethylene terephthalate film having a thickness of about0.001 inch (0.0025 cm).

The photosensitive elements useful in the invention will comprise atleast one photosensitive layer. The photosensitive layer may be eitherpositive or negative working as disclosed in "Light Sensitive System" byJaromir Kosar, John Wiley & Sons (1965), deForest, supra, and Coombs,supra. The layer may be applied to the substrate either as a coatedliquid or laminated as a dry film element. A particularly preferred,photosensitive polymeric layer is a photohardenable layer prepared frompolymeric components (binders), monomeric components, initiators andinhibitors. A top support or cover sheet may be present during exposureprovided it does not interfere with this step. Support and cover sheetsare well known in the art. A several layered support or cover sheet maybe used also.

Suitable binders which can be used as the sole binder or in combinationwith others include the following: polyacrylate and alpha-alkylpolyacrylate esters, e.g., polymethyl methacrylate and polyethylmethacrylate; polyvinyl esters, e.g., polyvinyl acetate, polyvinylacetate/acrylate, polyvinyl acetate/methacrylate and hydrolyzedpolyvinyl acetate; ethylene/vinyl acetate copolymers; polystyrenepolymers and copolymers, e.g., with maleic anhydride and esters;vinylidene chloride copolymers, e.g., vinylidene chloride/acrylonitrile;vinylidene chloride/methacrylate and vinylidene chloride/vinyl acetatecopolymers; polyvinyl chloride and copolymers, e.g., polyvinylchloride/acetate; saturated and unsaturated polyurethanes; syntheticrubbers, e.g., butadiene/acrylonitrile, acrylonitrile/butadiene/styrene,methacrylate/acrylonitrile/butadiene/styrene copolymers,2-chlorobutadiene-1,3 polymers, chlorinated rubber, andstyrene/butadiene/styrene, styrene/isoprene/styrene block copolymers;high molecular weight polyethylene oxides of polyglycols having averagemolecular weights from about 4,000 to 1,000,000; epoxides, e.g.,epoxides containing acrylate or methacrylate groups; copolyesters, e.g.,those prepared from the reaction product of a polymethylene glycol ofthe formula HO(CH₂)_(n) OH, where n is a whole number 2 to 10 inclusive,and (1) hexahydroterephthalic, sebacic and terephthalic acids, (2)terephthalic, isophthalic and sebacic acids, (3) terephthalic andsebacic acids, (4) terephthalic and isophthalic acids, and (5) mixturesof copolyesters prepared from said glycols and (i) terephthalic,isophthalic and sebacic acids and (ii) terephthalic, isophthalic,sebacic and adipic acids; nylons or polyamides, e.g., N-methoxymethylpolyhexamethylene adipamide; cellulose esters, e.g., cellulose acetate,cellulose acetate succinate and cellulose acetate butyrate; celluloseethers, e.g., methyl cellulose, ethyl cellulose and benzyl cellulose;polycarbonates; polyvinyl acetal, e.g., polyvinyl butyral, polyvinylformal; polyformaldehydes.

For aqueous development the binder should contain sufficient acidic orother groups to render the composition processible in aqueous developer.Useful aqueous-processible binders include those disclosed in U.S. Pat.No. 3,458,311 and in U.S. Pat. No. 4,273,857. Useful amphoteric polymersinclude interpolymers derived from N-alkylacrylamides ormethacrylamides, acidic film-forming comonomer and an alkyl orhydroxyalkyl acrylate such as those disclosed in U.S. Pat. No. 4,293,635which is incorporated herein by reference.

It is preferred that the photosensitive layer be relatively harder thanthose which generally have been commercially available. Greater hardnessof the layer provides greater dimensional stability and there is lessrequirement for a cover or support film.

Suitable monomers which can be used as the sole monomer or incombination with others include the following: t-butyl acrylate,1,5-pentanediol diacrylate, N,N-diethylaminoethyl acrylate, ethyleneglycol diacrylate, 1,4-butanediol diacrylate, diethylene glycoldiacrylate, hexamethylene glycol diacrylate, 1,3-propanediol diacrylate,decamethylene glycol diacrylate, decamethylene glycol dimethacrylate,1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate,glycerol diacrylate, tripropylene glycol diacrylate, glyceroltriacrylate, trimethylolpropane triacrylate, pentaerythritoltriacrylate, polyoxyethylated trimethylolpropane triacrylate andtrimethacrylate and similar compounds as disclosed in U.S. Pat. No.3,380,831, 2,2-di(p-hydroxyphenyl)-propane diacrylate, pentaerythritoltetraacrylate, 2,2-di-(p-hydroxyphenyl)-propane dimethacrylate,triethylene glycol diacrylate,polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propane dimethacrylate,di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-methacryloxyethyl) ether of bisphenol-A,di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-acryloxyethyl) ether of bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrachloro-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A,di-(3-methacryloxy-2-dydroxypropyl) ether of 1,4-butanediol,di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid,triethylene glycol dimethacrylate, polyoxypropyltrimethylol propanetriacrylate (462), ethylene glycol dimethacrylate, butylene glycoldimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetrioltrimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate,pentaerythritol trimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate,pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate,1,5-pentanediol dimethacrylate, diallyl fumarate, styrene,1,4-benzenediol dimethacrylate, 1,4-diisopropenyl benezene, and1,3,5-triisopropenyl benzene.

In addition to the ethylenically unsaturated monomers mentioned above,the photohardenable layer can also contain at least one of the followingfree radical-initiated, chain-propagating, addition-polymerizable,ethylenically unsaturated compounds having a molecular weight of atleast 300. Preferred monomers of this type are an alkylene or apolyalkylene glycol diacrylate prepared from an alkylene glycol of 2 to15 carbons or a polyalkylene ether glycol of 1 to 10 ether linkages, andthose disclosed in U.S. Pat. No. 2,927,022, e.g., those having aplurality of addition polymerizable ethylenic linkages particularly whenpresent as terminal linkages. Especially preferred are those wherein atleast one and preferably most of such linkages are conjugated with adouble bonded carbon, including carbon double bonded to carbon and tosuch herteroatoms as nitrogen, oxygen and sulfur. Outstanding are suchmaterials wherein the ethylenically unsaturated groups, especially thevinylidene groups, are conjugated with ester or amide structures.

Preferred free radical-generating addition polymerization initiatorsactivatable by actinic light and thermally inactive at and below 185° C.include the substituted or unsubstituted polynuclear quinones which arecompounds having two intracyclic carbon atoms in a conjugatedcarbocyclic ring system, e.g., 9,10-anthraquinone,1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone,2-ethylanthraquinone, 2-tert-butylanthraquinone,octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone,1,2-benzanthraquinone, 2,3-benzanthraquinone,2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone,1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone,2-phenylanthraquinone, 2-3-diphenylanthraquinone, sodium salt ofanthraquinone alpha-sulfonic acid, 3-chloro-2-methylanthraquinone,retenequinone, 7,8,9,10-tetrahydronaphthacenequinone, and1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione. Other photoinitiatorswhich are also useful, even though some may be thermally active attemperatures as low as 85° C., are described in U.S. Pat. No. 2,760,863and include vicinal ketaldonyl alcohols, such as benzoin, pivaloin,acyloin ethers, e.g., benzoin methyl and ethyl ethers;α-hydrocarbon-substituted aromatic acyloins, including α-methylbenzoin,α-allylbenzoin and α-phenylbenzoin. Photoreducible dyes and reducingagents disclosed in U.S. Pat. Nos. 2,850,445; 2,875,047; 3,097,096;3,074,974; 3,097,097; and 3,145,104 as well as dyes of the phenazine,oxazine, and quinone classes; Michler's ketone, benzophenone,2,4,5-triphenyl-imidazolyl dimers with hydrogen donors, and mixturesthereof as described in U.S. Pat. Nos. 3,427,161; 3,479,185; and3,549,367 can be used as initiators. Similarly the cyclohexadenonecompound of U.S. Ser. No. 271,241 filed June 8, 1981, U.S. Pat. No.4,341,860 are useful as initiators. Also useful with photoiniators andphotoinhibitors are sensitizers disclosed in U.S. Pat. No. 4,162,162.

Thermal polymerization inhibitors that can be used in photopolymerizablecompositions are: p-methoxyphenol, hydroquinone, and alkyl andaryl-substituted hydroquinones and quinones, tert-butyl catechol,pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprouschloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine,nitrobenzene and dinitrobenzene, p-toluquinone and chloranil. Alsouseful for thermal polymerization inhibitors are the nitrosocompositions disclosed in U.S. Pat. No. 4,168,982.

Various dyes and pigments may be added to increase the visibility of theresist image. Any colorant used, however should preferably betransparent to the actinic radiation used.

The preferred process of this invention will now be described inreference to the Figures in which the sensitized substrate is preparedas described in Example 1 of European Patent Application No. 81104013.8with either one or both sides of substrate bearing a solidphotosensitive layer.

With reference to FIGS. 1 and 2 shown in front and side elevation,respectively, is a circuit board exposure apparatus generally indicatedby reference character 20 adapted to register a circuit board indicatedby the reference character B (FIG. 2) with one or two flexible filmelements, or "photomasks" and thereafter expose one or both sides of theboard. In the preferred embodiment, the board is registered and exposedwhile in an upright or substantially vertical orientation. It should beunderstood that FIGS. 1 and 2 are stylized assembly views intended toimpart a general overview of the location of the various functionalelements which comprise the apparatus 20. Accordingly some elementspresent in one view are omitted in the other to afford clarity ofillustration. Detail views of various functional elements are set forthin other Figures.

As shown in FIGS. 1 and 2, the circuit board exposure apparatus 20comprises a framework 23 which supports the various functional elementsof the apparatus, an exposure unit 28 mounted to the framework 23, aregistration arrangement 30 for registering a circuit board with one ortwo flexible photomasks, a clamp arrangement 32 for securely engagingthe registered board and photomask(s), a board displacing arrangement 36for moving the registered board B and photomask(s) from, for example, aregistration position (located beneath the exposure unit 28 whenoperating in the preferred embodiment) to an exposure position withinthe exposure unit 28, a laminating arrangement 38 for laminating thephotomask(s) to the surface of the board as the engaged board andphotomask(s) are moved by the board displacing arrangement 36, and anapplicator arrangement 40 disposed in a trough 41 (FIG. 2) adapted toapply a liquid to each surface of the board B as a photomask islaminated thereto. A photomask take-up arrangement 42 (FIG. 2) isprovided to let-out and reel-in the photomask(s) as the registered boardand photomask(s) are moved. In addition, a board conveyor arrangement 44(FIG. 1) is mounted to the framework 23 and is operative to sequentiallyconvey boards to be laminated into a board transfer arrangement 46. Theboard transfer arrangement 46 is pivotally mounted with respect to theframework 23 and is operative in the preferred embodiment to transferboards from the conveyor 44 into the registration position and toreceive and transfer exposed boards to a suitable collection arrangement(not shown). A suitable electrical control network is interconnectedwith the various drives, actuators and sensors discussed herein tocontrol the operation of the board exposure apparatus 20. The controlnetwork may be physically mounted to the framework 23 at any convenientposition. In the preferred embodiment, the board displacing arrangement36, the board conveyor arrangement 44 and the board transfer arrangement46 are disposed substantially upright but slightly inclined (at aboutten to twency degrees) with the vertical.

FIG. 3 is a perspective view of a photomask carrier assembly generallyindicated by reference character 50 used in the circuit board exposureapparatus 20 of the present invention. The assembly 50 includes acarrier bar 52 provided at suitable locations thereon with registrationholes 54 and with openings 55 sized to receive clamp fingers 214(discussed in connection with FIG. 4). Since most of the structuralelements and features discussed herein are symmetrical about thevertical centerline VCL of the apparatus 20, like reference numerals areused to indicate corresponding elements or features on each side of thevertical center line. The carrier bar 52 is selected to exhibit athickness dimension 56 that is substantially equal to the thicknessdimension T of the circuit board B to be exposed. The board B isprovided with registration apertures A.

Depending in a parallel hinged relationship from each lateral surface ofthe carrier bar 52 are flexible film elements or photomasks 58. Theupper edges of each photomask 58 are hingedly connected by any suitablemeans of attachment to the carrier bar 52, e.g., by tape, in a precisemanner so that corresponding image features on the photomasks 58 (shownschematically by the reference character F) are in register to eachother by virtue of their precise connection to the carrier bar 52. This,in turn, locates the features relative to the registration holes 54. Asused herein the term "photomask" means a flexible sheet element havingareas which are transparent to radiation actinic to the photosensitivelayer and complimentary areas which are effectively opaque to thatradiation, the opaque and transparent area defining the complementaryimage features to be transferred to the photosensitive layer. Eachphotomask 58 is provided with registration apertures 62 for a purposediscussed herein.

FIGS. 4A, 4B, 5A and 5B show plan and front elevation views of the boardregistration arrangement 30 and of the board clamp arrangement 32.Section views of these elements are shown in FIGS. 6 and 7. The boardregistration arrangement 30 comprises a backbar 70 having a locating pin72 near each lateral end thereof and a front bar 76 reciprocally movablein the direction of arrows 77 with respect to the backbar 70 in a planeparallel to the plane of FIGS. 4A and 4B. The pin 72 shown in FIG. 5B isdiamond shaped to accommodate thermal expansion between the backbar 70and the differential carrier bar 52 of the photomask carrier assembly50. As perhaps best seen in conjunction with FIG. 6, the front bar 76 isprovided with registration pins 78 at predetermined locations thereon,the registration pins 78 projecting toward the backbar 70. The front bar76 is also provided with locating openings 82 at locations on the frontbar 76 which confront the registration pins 78 projecting from thebackbar 70.

The backbar 70 is an elongated member having a generally rectanguloidconfiguration with the lower end of the backbar 70 having a taperedflange portion 86 thereon (FIG. 6). As seen in FIG. 6 the boundary ofthe flange 86 is provided with a radius 88 arranged to match the radiusof the rolls used in the laminating arrangement 38 for a purposediscussed in connection with FIGS. 9 and 10. A bore 90 is providedthrough the flange 86 in locations on the backbar 70 confrontationallycorresponding to the registration pins 78 disposed on the front bar 76.

The locating pins 72 are secured to the backbar 70 by any attachmentmechanism, shown in FIGS. 4A and 4B by a mounting bracket 94 arranged tofacilitate replacement of the pins 72 due to wear or abuse. The backbar70 is cut out, as at 102 (FIGS. 5A and 5B), to accommodate a rod 148which is operatively associated with the front bar 76. The laterallyoutward ends of the backbar 70 are connected to a carriage 252 which isincluded in the board displacing arrangement 36 discussed herein. Nearthe center of the backbar 70, clamp support brackets 110 (FIG. 4) aremounted to the backbar 70 by bolts 112. The backbar 70 has clamp accessapertures 114 provided in the vicinity of the brackets 110 toaccommodate clamp fingers 214 which are a part of the board clampingarrangement 32 also discussed herein.

The front bar 76 is an elongated rectanguloid member which is attached,as by bolts 124 (FIG. 4), to a mounting frame 122. The frame 122 isadapted to accept interchangeable front bars 76 which carry variousarrangements of registration pins 78. (The other structural elements ofthe apparatus, as the backbar 70 and the clamp bar 208, are providedwith a suitable array of apertures, as the apertures 90 and 238 (FIG.6), respectively, to accommodate the various arrays of the registrationpins 78). The laterally outward ends of the front bar 76 are connectedto a front block 128 by bolts 130. The upper and lower surfaces of thefront block 128 are flexibly connected to a rear block 132 by upper andlower leaf springs 136 and 138, respectively. The attachment of thesprings to the front block 128 is accomplished by the bolts 130, whilethe same springs are secured to the rear block 132 by bolts 142. Therear block 132 is connected to a rod 148 which extends rearwardly fromthe rear block 142. The rod 148 is connected to the block 132 by meansof a bolt 150 which extends into the rod 148 through a counterboreprovided in the rear block 132. The back end of each of the rods 148 isconnected to an elongated push bar 156 (FIG. 4) by a bolt 158 whichextends through a counterbore provided in the push bar 156.

One lateral end of the push bar 156 (the left end as viewed in FIG. 4A)extends past its interconnection to its associated rod 148 where it ispivotally connected to one end of a connecting rod 162 (see also, FIG.8). The connecting rod 162 is pivotally connected at its other end to amember 164. The member 164 is itself pivotally connected to a crank arm166 which fits about the drive shaft 168 of a rotary pneumatic actuator170. The actuator 170 is supported on a plate 172 which is secured bybolts 174 to side plates 23S which in turn are secured to and form partof the framework 23. The plate 172 is provided with cutouts 175 (FIG. 4)through which passes a belt 258 which is a part of the board displacingarrangement 36. Rotation of the actuator drive shaft 168 in theappropriate direction results in the reciprocating rectilinear motion,in the direction of the arrows 77, which brings the front bar 76 and theregistration pins 78 thereon toward and away from registrationengagement with the backbar 70. Suitable for use as the actuator 170 isa device manufactured by Ex-Cello Corp. and sold under model numberS-1251-V. A locating magnet 176 is mounted to the push bar 156 andcooperates with a Hall Effect sensor 178 mounted on a bracket 180connected to the side plate 23S to provide signals PIN IN and PIN OUT onlines 182 and 184, respectively. These signals are used by the controlnetwork. Suitable for use as the sensor 178 is a device manufactured byMicroswitch Inc. and sold under model number 413SR10 while the magnet176 is available from the same company under model number 101MG7.

As seen from FIGS. 4 and 7, the rod 148 is supported by front and rearbearing assemblies 186 and 188, respectively, disposed wtihin a bearinghousing 190. The bearing housing 190 is flexibly connected to the plate172 through a flat spring 192 (FIGS. 7 and 8) by bolts 194 and 196. Abrace plate 198 is secured between the bearing housings 190 at each endof the apparatus by bolts 202 (FIG. 8). Due to the flexible couplingafforded by the springs 136 and 138 (FIG. 5A) and the flat springs 192,it may be appreciated that front bar 76 may deflect upwardly anddownwardly in the planes of FIG. 5 and laterally in the plane of FIGS. 4and 5 to permit registering engagement with the backbar 70.

The clamp arrangement 32 (believed best seen in FIGS. 4 and 6) includesa clamp bar 208 having openings 210 disposed near each end thereof. Theopenings 210 are spaced apart on the clamp bar 208 at the same spacingas the locating pins 72 on the backbar 70. Thus, the clamp bar 208 maybe mounted onto the locating pins 72 and are movable thereon withrespect to the backbar 70. The fingers 214 extend rearwardly through theclamp access apertures 114 in the backbar 70. The clamp fingers 214 arenotched, as at 215 (FIG. 6), so as to engage the clamp bar 208. Theportion of the clamp fingers 214 disposed behind the backbar 70 have anotch 217 sized to receive a post 218. The post 218 is connected to oneleg of an L-shaped crank 220 which is pivotally mounted to the clampsupport bracket 110 by a pin 222. The other end of one of the L-shapedcranks 220 (shown in FIG. 4A) is pivotally attached, as at 224, to apiston rod 228 of an activating cylinder 230. The other end of the otherof the cranks 220 (shown in FIG. 4B) is connected, as at 225, to aclevis 231 which is attached to the cylinder 230. Both the rod 228 andthe cylinder 230 are movable in the direction of arrows 232 with respectto the machine frame 23 to reciprocate the clamp bar 208 toward and awayfrom the backbar 70.

The lower end of the clamp bar 208 has a flange portion 236 thereon(FIG. 6). A bore 238 extends through the flange 236 in alignment withthe bore 90 extending through the flange 86. A portion of the flange isrounded, as at 240, to conform to the periphery of the rolls used in thelaminating arrangement 38. Movement of the clamp bar 208 toward thebackbar 70 serves to exert a clamping force acting in the direction ofthe arrow 242 (FIG. 6) tending to securely grip a circuit board andphotomasks registered therewith between the clamp bar 208 and thebackbar 70. Suitable for use as the actuating cylinder 230 is adouble-acting pneumatic cylinder such as that manufactured by Bimba Mfg.Co. and sold under model number 09-DX. Pneumatic pressure is introducedinto the cylinder 230 by appropriate fluid lines 246 in response to asuitable signal from the control network 48.

In the assembled relationship shown in the Figures, the photomaskcarrier assembly 50 (FIG. 3) is mounted to the backbar 70 with thelocating pins 72 on the backbar extending through the registration holes54 and the clamp fingers 214 extending through the openings 55 in thecarrier assembly 50. The clamp bar 208 may be loosely mounted onto thesame pins 72 and clamp fingers 214 outwardly of the carrier assembly 50to thereby sandwich the carrier and photomasks between the backbar 70and the clamp bar 208.

The board displacing arrangement 36 (FIGS. 4, 5 and 7) includes acarriage 252 connected to each end of the backbar 70 by bolts 254. Thelower rear surface 256 of the carriage 252 is rounded (FIG. 7) as at 256to conform to the rolls in the laminating arrangement 38. The bolts 254also engage a timing belt 258 to secure the backbar 70 to the belt 258.The belt 258 is trained over an upper pulley 260 (FIG. 1) disposed abovethe exposure unit 28 and a lower drive pulley 262. The carriage 252 hasfollower rollers 266 (FIGS. 4 and 7) extending sidewise therefrom. Therollers 266 are captured in tracks 268 supported from the sideplates23S. The tracks 268 are inclined at a slight angle to the vertical butmay be characterized as being in a substantially upright orientation.

The upper pulley 260 (FIG. 1) is secured to a shaft 272 which isrotationally mounted on suitable bearings 269 between the two hollowupstanding support posts 23P secured to the framework 23. The lowerpulley 262 is secured to a shaft 278 (also seen in FIGS. 9 and 10) whichis supported for rotational movement by bearings 280 mounted to thesideplates 23S. The sideplates 23S are supported on brackets 23B fromthe posts 23P. The shaft 278 is driven by a reversible electric motor282 mounted on the bracket 23B. The motor 282 is connected by a belt 284in a driving relationship with a pulley 286 (also seen in FIGS. 9 and10) connected to the shaft 278. Position signals for use by the controlnetwork are provided from a board displacement position encoder 288(FIG. 2) connected to the drive motor 282. Board position signals arecarried on lines 290A, 290B, 290C and 290D. Suitable for use as theencoder 288 is a device sold under model number IMI-205-41-0 byInternational Micro Industries, Cherry Hill, N.J.

The board displacing arrangement 36 hereinabove described is operativeto vertically displace the backbar 70, the photomask carrier assembly 50and the clamp arrangement 32 mounted thereon to various locations withrespect to the frame 23. In one position the clamp bar 208 is madeaccessible to an operator and may be removed, enabling the operator toeffect replacement of the photomask carrier assembly. This position isindicated by a signal on the line 290D. In another position, the boardregistration position corresponding to a signal on the line 290B, thecircuit board is registered to the photomasks in a manner to bedescribed. Thereafter, the board displacing arrangement 36 is operativeto move the registered and clamped board and photomasks through theboard laminating arrangement from which the registered and clamped boardand photomasks are displaced to a board exposure position correspondingto a signal on the line 290C. The board, after exposure, is loweredbelow the registration position to a position corresponding to a signalon the line 290A during which motion the exposed board is returned tothe board transfer arrangement 46.

With reference to FIGS. 9 and 10, respectively shown is a plan view anda front elevation of the laminating arrangement 38 used in the circuitboard exposure apparatus of the present invention. The laminatingarrangement comprises a front and a rear laminating roll 302 and 304,respectively, mounted on associated shafts 308 and 310. Each of therolls 302 and 304 is coated with one-eighth inch thick neoprene rubber,90 Shore A durometer. Each roll is mounted for rotational movement withrespect to its associated drive shaft on bearings 312 and 314,respectively.

As seen from FIGS. 9 and 10 the drive shaft 310 for the rear roll 304extends outwardly past the end of the roll through aligned bores 318 and324 respectively provided in a first link member 320 and a couplingmember 326. The shaft 310 is connected for rotation with a driven pulley332 (FIG. 9) outwardly from one of the coupling member 326. Bearings 334and 336 are respectively provided to line the aligned bores 318 and 324to permit rotational movement of the shaft 310 with rspect to the firstlink 320 and the coupling 326.

The driven pulley 332 is connected by a timing belt 346 with a drivepulley 348 (FIG. 10) connected to the shaft 278. The shaft 278 extendsinwardly of the apparatus 20 past the drive pulley 348 and through abore 350 provided in the coupling member 326. A bearing 352 is disposedwithin the bore 350 to permit pivotal motion of the coupling member 326with respect to the shaft 278.

The first link member 320 has a bore 360 (FIG. 9) which aligns with abore 366 formed in a second link member 364. A pivot pin 370 projectsthrough the aligned bores 360 and 366 to define a pivotally articulableconnection between the link members 320 and 364. The bores 360, 366, and370 are provided with suitable bearings. The second link member 364 isitself pivotally mounted with respect to the side plates 23S on pivotpins 371 supported in bores 372 and 374 in the side plates 23S andsecond link, respectively.

The pivot pin 370 is pivotally connected to the end of a piston rod 376of a pneumatic actuator 382 mounted to the frame 23. The actuator 382 iscontrolled by a signal from the control network 48 on a line 386.Suitable for use as the actuator 382 is a device manufactured by BimbaMfg. Co. and sold under model number 09-DX.

A bore 390 extends through the first link member 320 substantiallyintermediate the bores 318 and 360. A spring loader roller 392 ismounted within the bore 390, the roller 392 abutting against the rearroll 304. The force exerted by the roller 392 against the roll 304 iscontrolled by a spring 396. The two bar linkage formed from the links320 and 364 is constrained so it cannot pass through center by a stop397 (FIG. 7) suitably connected to the frame 23 in any convenientlocation.

As seen from FIGS. 5A and 9 the drive shaft 308 extends past the ends ofthe front roll 302 through a bore 402 provided at one end of one arm ofan L-shaped coupling member 406. A bearing 410 lines the bore 402 topermit the shaft 308 to rotate with respect to the coupling 406. Thebearing 410 has an annular protrusion 414 thereon to permit the roll 302to align itself parallel to the roll 304 without deflecting the shaft308 in the event of any misalignment of the axis of the roll 304 and thebores 402.

A driven pulley 420 is connected to the shaft 308 outwardly of thecoupling 406. A timing belt 424 connects the pulley 420 to a drivepulley 428 (FIG. 5A). The drive pulley 428 is fixed to a shaft 432 whichis mounted for rotation with respect to the side plate 23S by a bearing436. The shaft 432 extends into a bore 438 provided at the joint of thearms of the coupling 406. The bore 438 is lined with a bearing 442 topermit the coupling 406 to pivot about the shaft 432. As seen in FIG. 9,the end of the other arm of the L-shaped coupling 406 has a bore 448extending therethrough. The bore 448 is lined with a bushing 450 whichreceives a bar 454. The bushing 450 has a protrusion 456, similar to theprotrusion 414. An actuator 458 (FIG. 7), similar to the actuator 382 isconnected midway along the bar 454. The actuator 458 responds to thesignal (OPEN ROLLS) output on the line 386 from the control network toopen the rolls 302 and 304. A Hall Effect sensor 459 (FIG. 9) similar tothe sensor 178 (FIG. 4A) is mounted on a suitable bracket attached tothe frame 23 and a magnet 460 (similar to the magnet 176 (FIG. 4A) ismounted to the coupling member 406. The sensor 459 and magnet 460 areoperative to provide signals on lines 462 and 463 respectivelyrepresentative of the rolls being in the open and closed positions.

A drive gear 464 (FIG. 10) is connected for rotation with the shaft 278.A driven gear 468 is fixed to the shaft 432 for rotation therewith. Thedrive gear 464 is intermeshed with the driven gear 468. As seen in FIG.6, 7 and 10, a transmitter 476T and a receiver 476R are convenientlymounted to the frame and are arranged to communicate along a ray path477 (through appropriately located apertures in the backbar, clamp andfront bars). When a board B interdicts the ray path 477 defined betweenthe transmitter and receiver a signal BOARD IN POSITION is output on aline 478 to the electrical control network. Suitable for use as thetransmitter is a device sold by Banner Controls Inc. under model numberRT400B while the receiver is available from the same company undernumber LR400.

The drive train for the laminating arrangement 38 may be traced withreference to FIGS. 1, 5A, 9 and 10. Rotation of the shaft 278 by themotor 282 rotates the pulley 262 and, therefore, the pulley 348 (FIG.10) at the same angular velocity as the pulley 262. The pulley 348,through the belt 346, drives the pulley 332. In turn, the shaft 310,connected to the pulley 332, rotates therewith since the pulleys 332 and348 have identical pitch diameters. In this manner the rear shaft 310exhibits the same angular velocity as the pulley 262. By making thepitch diameter of the pulley 262 equal to the outside diameter of theroll 304, the surface speed of the roll 304 equals the linear speed ofthe backbar 70 as it is raised by the board displacing arrangement 36.However, since the roll 304 rides on the bearing 314, any slippagebetween the roll 304 and the shaft 310 may be accommodated.

In the case of the roll 302, rotation of the shaft 278 rotates the drivegear 464 therewith. The drive gear 464 engages the driven gear 468 whichrotates the shaft 432. The gears 464 and 468 have equal teeth. The shaft432 drives the pulley 428, which through the belt 424 rotates the pulley420. The pulleys 420 and 428 have identical pitch diameters. Rotation ofthe pulley 420 thus turns the shaft 308 at the same angular velocity asthe shaft 310 and the pulley 262. By making the outside diameter of theroll 302 equal to that of the roll 302 the front roll 302 runs at thesame surface speed as the roll 304. Again, due to the provision of thebearings 312, slippage between the roll 302 and its associated shaft 308may be accommodated.

The rolls 302 and 304 may be opened and closed in the following manner.To open the rolls to the position shown in FIG. 7 an actuating force isapplied on the line 386 to the actuator 382 (FIG. 9) connected to thefirst link member 320 and to the actuator 458 mounted to the bar 454(FIG. 9). The actuators respond by imposing forces in the directions ofarrows 474 (FIG. 7) respectively drawing apart the rolls 302 and 304.The front roll 302 is retracted by the pivotal action of the L-shapedcoupling 406 about the shaft 432. The rear roll 304 is retracted by theflexing of the two-bar linkage formed of the members 320 and 364. Thisflexure causes the shaft 310 to be drawn rearwardly with the coupling326 pivoting on the shaft 278 to accommodate this movement. Impositionof forces in directions opposite to the arrows 474 restores the rolls302 and 304 to the closed position. The great mechanical advantage ofthe two bar linkage insures that the roll 304 always closes to a fixedposition with the linkage fully extended. The roll 302 will close to avarying position to accommodate various board thicknesses. Thus, theroll 304 forms a fixed datum in the closed position.

The registration and lamination of a circuit board character B may nowbe understood. Prior to board registration, the board B is liftedupwardly through the open rolls 302 and 304 (shown in FIG. 7) by theboard transfer arrangement 46 to be described. The board B is liftedbetween the photomasks 58 depending from the photomask carrier bar 52.The photomask carrier bar 52 is previously mounted to the locating pins72 on the backbar 70, and the clamp bar 208 has been set in place. Theseevents have occurred in the photomask replacement position, as earlierdiscussed. The displacing arrangement 36 moves the backbar, photomaskcarrier and clamp bar to the registration position.

When the upper edge of the board B is generally in the vicinity of theregistration position, as detected by the transmitter/receiverarrangement 476, its upward motion is halted. The front bar 76, havingthe registration pins 78 thereon, is moved toward the backbar 70 andclamp bar 208 in the direction 77 by the action of the actuator 170(FIGS. 4A and 4B). As the front bar 76 moves toward the backbar 70 andthe clamp bar 208, the locating pin 72 on the backbar enters thelocating openings 82 provided in the front bar 76 whereby a precisealignment is accomplished. Substantially simultaneously with thisoccurrence the registration pins 78 sequentially (1) enter the openings238 (in the flange 236 on the clamp bar 208), (2) the apertures 62 inthe front photomask 58, (3) the registration apertures A provided in theboard B, (4) the apertures 62, (5) the rear photomask 58, and (6) theopenings 90 in the flange 86 on the backbar 70. It is noted that of allof the above listed apertures only those in the board B precisely matchthe pins 78. All other apertures are slightly oversize. The insertion ofthe locating pins 72 into the locating openings 82 in the front bar 76serves to place the front and backbars in precise register. Theinsertion of the registration pins 78 with the board brings the board inregister (FIG. 7). In this manner the board B is precisely registeredbetween the photomasks carried on the carrier assembly. It is preferredthat when the board is lifted into the registration position it isplaced such that the board rides up on the beveled end of theregistration pins 78 as these pins enter the board, thus lifting theboard B free of the transfer arrangement during the registrationprocess.

With the board and photomasks registered, the clamp fingers 214 areactivated by the actuator 230 thus securely gripping the registeredboard and photomasks. The front bar 76 is then retracted to the initialposition and the clamped and registered board and photomasks lowered tothe laminating position by the board displacement arrangement 36. Whenthe clamped and registered board and masks reach the laminatingposition, the nip rolls 302 and 304 are closed in the manner discussed.The surface of the rolls is received by the rounded portions 88 and 240provided in the flange 86 on the backbar 70 and the flange 236 on theclamp bar 208, respectively. The board displacement arrangement 36 isactuated, lifting the clamped board and photomasks from the laminatingto the exposure position. As discussed earlier, the surface speed of thelaminating rolls 302 and 304 matches the speed at which the clamped andregistered board and photomasks are displaced.

As the board B and photomasks are laminated, water is applied to bothsurfaces of the board by the applicator arrangement 40. The applicatorarrangement 40 comprises two closed ended, hollow tubes 480A and 480B ofcircular cross section mounted to the sideplates 23S of the framework23. The tubes 480 are aligned with their axes parallel to the axis ofthe shaft 310 and arranged to lie directly beneath the rolls 308 and310, respectively. The tubes 480 extend the full length of the rolls 308and 310. An array of fine holes 482 (preferably approximately 0.020 inchdiameter) are drilled at predetermined spacings (approximately 0.25inch) into each of the tubes 480 in a line parallel to the tube axis.The tubes 480 are installed such that the hole array in the tube 480A isdirected toward the roll 304 while the array of holes in the tubes 480Bis directed toward the roll 302. With this orientation water sprayedfrom these arrays impinges on both photomasks 58 and/or both sides ofthe board B. The trough 41 is arranged to catch liquid dripping fromeither of the rolls 308 and 310. The trough 41 is provided with anaperture 484 through which the board B passes. A second trough 41' (FIG.2) is disposed beneath the conveyor arrangement 46 to trap liquidpassing through the aperture 484.

Liquid is circulated by a pump 486 through a filter 488 (typically onemicron) and is carried through any suitable conduits to the spray tubes480. Additional water may occasionally be added as necessary.

The ends of the photomasks 58 opposite their attachment to the photomaskcarrier bar 52 are connected to the photomask take-up arrangement 42. Aside elevation view of one of the take-up rolls 502 used in take-uparrangement 42 is shown in FIG. 12. It is to be understood that asimilar roll 502 is used for each photomask. The rolls 502 are mountedin any convenient location on the side frame 23S. The roll 502 includesa tubular portion 504 closed at each end by a cover plate 506. The roll502 is mounted to a shaft 510 extending centrally and axiallytherethrough. The shaft is supported in each cover plate 506 by anelastomeric bearing 514 which permits the take-up roll 502 to deflect toaccommodate any forces imposed thereon. The ends of the shaft 510 aresupported by bushings 516 (only one of which is shown in FIG. 12) whichline openings provided in the side plates 23S. One end of the shaft 510is connected to a pulley 518 which is driven by a timing belt 520 from apulley 524 connected to a suitable drive motor 528. The motor 528 ismounted on a suitable bracket 530 supported by the side plate 23S.Motive energy is transmitted to the roll 502 by a crank 532 affixed tothe shaft 510. The crank 532 carries a pin 536 which engages an opening538 provided in the cover plate 506. The take-up rolls 502 are driven ina direction and at a speed compatible with the movement of the boarddisplacing arrangement to either take-up or let-out (as the case may be)the photomasks as the photomasks move with the board to which they areregistered and clamped. Suitable for use as the motor 528 is a devicemanufactured by Bodine and sold under model number NCI-35.

The exposure unit 28 (FIGS. 1 and 2) contains sources operative toprovide actinic radiation to the surface of the board through thephotomasks registered therewith while the board and photomasks are inthe exposure position. In the preferred case, the exposure unit 28includes a front and a rear half 540A and 540B (FIG. 2) which arepivotally mounted on posts 541 (FIG. 1) projecting from the frame posts23P. Each half of the exposure unit 28 preferably contains an array offluorescent lamps indicated by the character 542 each of which emitsubstantial amounts of radiation to which the photosensitive substrateon the board B is active. The halves of the exposure unit 28 arepivotally movable to provide access to the interior of the unit 28.Since the posts 23P are hollow, it is preferred that they serve ascooling fluid conduits to conduct a cooling fluid, as air, from blowers543 conveniently mounted to the framework. The air from the interior ofthe post 23P passes through an opening surrounded by a collar 544mounted to the posts 23P into the exposure unit 28. Suitable for use asthe blower is a device manufactured by Rotron and sold under modelnumber Vanguard VJ6016A52.

The board conveyor arrangement 44, shown in FIGS. 13A through 13C andFIG. 14, includes a lower support plate 602 mounted to the lowersuperstructure of the frame 23 in any convenient manner, as by brackets604 and bolts 606. An upper support plate 608 is supported away from,but in parallel relation to, the lower support plate 602 by brace bars610. The brace bars 610 are secured to the plates 602 and 608 by anysuitable means of attachment, such as the bolts 612. The lower plate 602is provided with cutouts 616 and 618 (FIGS. 13B and 13C) which permitoperating clearance for the board transfer arrangement 46 to bediscussed. An intermediate support plate 622 (FIG. 13C) is supported bybrace bars 624 away from the region of the lower support plate 602between the cutouts 616 and 618.

Conveyor drive rollers 630, 632, 634 and 636 are mounted to suitabledrive shafts 642, 644, 646 and 648, respectively. The shafts aresupported for rotation beneath the lower plate 602 by suitable brackets652. Also suitably mounted for rotation at predetermined positions alongthe lower plate 602 are idler rollers 656 through 672. A conveyor belt676 is trained around the conveyor drive rollers 630 and 632 and issupported by the idler rollers 656, 658, 660, 662 and 664. A secondconveyor belt 680 is trained around the drive roller 634 and the idlerrollers 666 and 668. A third conveyor belt 684 is trained over the driveroller 636 and the idler rollers 670 and 672. The belts 676, 680 and 684each include a groove 686 (FIG. 13D) which is adapted to support thelower edge of a circuit board B as it is horizontally conveyed by theconveyor arrangement 44 toward the board transfer arrangement 46 to bedescribed. Suitable at the belts 676, 680 and 684 are belts manufacturedby Eagle Belting Co. and sold under model number 3L Sec "Twin".

The shaft 644 (FIG. 13B) carries a pulley 690 which is connected by abelt 694 to a pulley 698 (not visible in FIG. 13C) mounted to the shaft646 (FIG. 13C). The shaft 646 also carries a second pulley 702 forwardlyof the pulley 698 (not shown). The pulley 702 is connected by a belt 706to a pulley 710 mounted to the shaft 648. The shaft 642 (FIG. 14)carries a pulley 716 which is connected by a belt 720 to the outputshaft of a brake/clutch mechanism 724 (FIG. 14) that is mounted to theframework 23. The brake/clutch mechanism is operatively associated witha horizontal conveyor drive motor 728 also mounted to the framework 23.Suitable for use as the motor 728 is a device manufactured by Bodine andsold under model number 44D581PM, while the brake/clutch mechanism 724may be that sold by Warner Company under model number Mod. Size EP-250.A shaft encoder 730, such as that sold by Opto Technology, Inc. undermodel number OTS0251 is connected to the shaft from the brake/clutch724. Output signals on a line 732 are provided from the encoder 730 tothe control network and serve as an indication of the horizontal speedof a board B carried by the conveyor arrangement 44. Motor controlsignals CONVEYOR MOTOR ON on a line 732 and CONVEYOR MOTOR DIRECTION ona line 734 are applied to the motor 728 from the control network. Inaddition, a clutch control signal HORZ. CLUTCH is applied on a line 740to the clutch 724. The clutch/brake 724 is arranged such that if theclutch is not engaged, the brake is automatically asserted.

The drive train for the lower conveyor belts 676, 680 and 684 may now beunderstood. Motive energy from the motor 728 is applied (when the clutch724 is engaged) to the pulley 716 to rotate the drive pulley 630. Thepulley 630 through the conveyor belt 676 drives the shaft 644 for theroller 632, which in turn drives the shaft 646 for the roller 634through the pulley 690, the belt 694 and the pulley 698. The shaft 646also drives the pulley 702, which through the belt 706 and the pulley710 drives the shaft 648 for the roller 636.

Each of the shafts 642, 644, 646 and 648 carries a bevel drive gear 744(FIG. 14) which is mated with a bevel driven gear 746 (FIG. 14) carriedby each of shafts 748, 750, 752 and 754. Each of these last-mentionedshafts are mounted at their lower ends for rotation with respect to thelower plate 602. The shafts 748, 750 and 754 are mounted at their upperends for rotation with respect to the upper plate 608. The upper end ofthe shaft 752 is mounted for rotation with respect to the intermediatesupport plate 622. Idler shafts 756 and 758 (FIGS. 13A and 13B,respectively) are also mounted for rotation between the plates 602 and608.

Pulleys 760, 762 and 764, 766 and 768 are respectively connected to theshafts 748, 756, 758, 750 and 754 for rotation therewith. A belt 772 istrained over the pulleys 760, 762 and 764. A belt 774 is trained overthe pulleys 766 and 768. As seen in FIG. 13E, the belts 772 and 774include a pointed edge 778 which is arranged to touch against the uppermargin of the circuit board B as it is carried along by the horizontalconveyor arrangement 44. Suitable for use as the belts 772 and 774 arebelts manufactured by Eagle Belting Co. and sold under model number A:"Hi-Ridge-Top". The shaft 750 also carries a roller 780 having a rimwhich defines a peripheral edge 782. A similar roller 784 which definesa peripheral edge 786 mounted to the shaft 752. The edges 782 and 786abut against the board B substantially midway along its height, but donot affect the photosensitive layer on the board.

An input sensor arrangement, comprised of a transmitter 788T and areceiver 788R output a signal BOARD INPUT on a line 790 to the controlnetwork. A centering sensor arrangement comprising a transmitter 792Tand receiver 792R is mounted on the vertical centerline VCL of theapparatus. A signal, BOARD CENTERED is applied from the receiver 792R tothe control network on a line 794.

The board transfer arrangement 46 is shown in FIGS. 15 and 16. Thetransfer arrangement 46 includes a pair of board lifting arms 800L and800R disposed on opposite sides of the vertical centerline VCL and apair of board lowering arms 804L and 804R respectively corresponding tothe arms 780. (The arm 804R is ot visible in the Figures) The lower endsof each of these four arms are secured to the periphery of a tube 806such that the angular spacing 808 (FIG. 16) between the axes of thecorresponding arms 800L and 804L or 800R and 804R remains fixed. Thetube 806 is rotationally mounted on suitable bearings 808 to a shaft810. The shaft 810 is itself rotationally mounted with respect tomounting plates 23R affixed to the frame 23.

Mounted for rotation with the shaft 810 laterally outwardly of the arms800 and 804 are bottom pulleys 812B, 814B, 816B and 818B. The upper endsof the arms in each pair of arms 800 and 804 are connected by a tubularmember 822 and 824 respectively. (The member 824 is not visible in thedrawings.) A shaft 826 and 828 is mounted for rotation within the tubes822 and 824, respectively. Top pulleys 814T and 816T are mounted toopposite ends of the shaft 826 for rotation therewith. Similarly, toppulleys 812T and 818T are mounted for rotation with opposed ends of theshaft 828. The corresponding top and bottom pulley are interconnected bybelts 830, 832, 834 and 836 respectively. Secured to each of the beltsat corresponding heights thereon is a board lifting carriage 838, 840,842 and 844, respectively. (The carriages 838 and 842 are not shown inFIG. 15 for clarity of illustration.) Each of the carriages are providedwith followers 846. The carriages 840 and 842 respectively ride alongtracks 852L and 852R secured to the outside surfaces of the arms 800.The followers on the carriages 838 and 844 respectively ride in tracks854L and 854R secured to the outside of the arms 804. The tracks 854 arebuilt-up in order to permit the carriaes 838 and 844 to ride outboard ofthe carriages 840 and 842. Each carriage is provided with fingers 858adapted to engage the lower edge of a circuit board B.

The shaft 810 is connected to a pulley 860 which is, in turn, connectedby a belt 862 to the output shaft of a brake/clutch mechanism 864similar to the brake/clutch mechanism 724. The brake/clutch mechanism isconnected to a driver motor 866, similar to the motor 728. A shaftencoder 868, similar to the encoder 730, is mounted to the output shaftfrom the brake/clutch 864. Signals representative of the location of thecarriages with respect to their arms are output from the encoder 868 tothe control network on a line 870. Motor control signals LIFT MOTOR ONand LIFT MOTOR DIRECTION are carried on lines 872 and 874 respectivelyfrom the control network. The clutch 864 receives a signal VERTICALCLUTCH on a line 865 from the control network.

When the motor 866 is energized and the clutch enabled, the carriages838, 840, 842 and 844 move together upwardly and downwardly (dependingupon motor direction). As seen from FIG. 16, the drive belt 832 for thecarriage 840 carries a member 876 which cooperates with a limit switch878 to generate a CARRIAGE DOWN position signal output on a line 880 tothe control network. Suitable for use as the limit switch 878 is adevice sold by Opto Technology, Inc. under model number OTS-251.

The arms 800 and 804 are movable from the board receiving position(shown in FIG. 16A) to a board deposit position (shown in FIG. 16B) byan actuator 884 connected between one of the arms 800 and the frame 23.Suitable for use as the actuator is a device manufactured by Bimba andsold under model number 09-DX. The actuator 884 is controlled by anoutput signal carried on a line 886 from the control network to displacethe mechanism to the deposit position wherein the exposed board may becarried away by any suitable means.

One of each pair of the arms 800 and 804 carries a magnet 890 and 892,respectively. Sensors 894 and 896 are mounted to the frame 23 inappropriate positions to respectively provide a BOARD RECEIVE positionsignal on a line 898 and BOARD DEPOSIT position signal on a line 902representative of the transfer arrangement occupying the receive anddeposit positions, respectively. These sensors arrangements are similarto the magnet 176 and the sensor 178 (FIG. 4A).

FIG. 17 is a highly stylized pictorial representation of the boardexposure apparatus 20 from which an understanding of the operation ofthe present invention may be obtained. In the following discussion, thefollowing initial conditions are assumed extant:

a photomask carrier 50 (FIG. 3) is mounted onto the locating pins 72projecting from the backbar 70;

the clamp bar 208 is open;

the exposure unit 28 is in a standby condition;

the front bar 76 carrying the registration pins 78 is disengaged frombackbar 70;

the laminating rolls 302 and 304 are open;

the applicator arrangement is operative to direct a spray of liquidtoward the path of the circuit board;

transfer arrangement 46 is in the board receiving position (FIG. 16)with the carriages occupying their lower positions with respect tolifting arms 800 and lowering arms 804; and

the board conveyor arrangement 44 is operative.

The first unexposed circuit board B having laminated photosensitivepolymer layers on each side thereof and at least two pin registrationapertures A therein is conveyed by the board conveyor arrangement 44into a position intermediate the pair of the lifting and lowering armsof the board transfer arrangement 46. As the board B is conveyed alongthe conveyor arrangement 44 its length is measured by the action of thesensors 788. The board B is centered with respect to the lifting arms800 by the action of the centering sensor 792. Once centered, the boardconveyor 44 is stopped and the board transfer arrangement 46 is pivotedto the board deposit position. During the movement of the board transfermeans the unexposed circuit board is picked up by the carriages on thelifting arms 800.

With the transfer arrangement 46 in the board deposit position thelifting arms thereof are disposed substantially vertically beneath theboard registration arrangement. The carriages on the lifting arms 800are activated lifting the board thereon upwardly through the openlaminating rolls 302 and 304. When the upper edge of the unexposed boardis in proximity to the registering arrangement the lifting thereof ishalted by operation of the board position sensor 476. The position ofthe carriages with respect to the arms is stored for later use. With theupper edge of the board proximal to the registering means, the front bar76 having the registration pins 78 thereon moves in the direction ofarrow 77 toward the backbar 70. The motion of the front bar 78 placesthe locating pins 72 into the openings 82 provided in the front bar 70.Substantially simultaneously with this occurrence the registration pins78 on the front bar enter the apertures 238 and 90 provided in the clampbar 208 and the backbar 70 respectively and through the registrationapertures provided in the photomasks 58 and the circuit board B. Whenthe registration pins 78 have fully engaged and registered the board Bwith respect to the photomasks 58. The clamp arrangement 32 is thereuponactivated, firmly gripping the registered board and photomasks betweenthe clamp part 208 and the backbar 70. The front bar 76 is returned toits initial position and the carriages on the lifting and lowering armsare returned to their lower position.

The board displacing arrangement 36 is activated to lower thenow-clamped and registered board and photomasks to the laminatingposition where the lower contoured radii of the backbar 70 and the clampbar 208 are in a position to abut against the rolls 302 and 304,respectively of the laminating arrangement 38. Upon reaching thisposition, the laminating rolls close. Upon reaching this position, thelaminating rolls close. The board displacing arrangement 36 is againactivated to lift the board and the photomasks 58 registered theretofrom the laminating position toward the exposure position. As the boardis displaced through the now-closed laminating rolls, the photomasks 58are laminated to the surface of the board B. Intimate contact betweenthe photomasks and each surface of the board B is achieved by the actionof the laminating rolls 302 and 304 squeezing excess liquid from betweenthe board and the photomasks as the board B is displaced therepast. Whenthe board and the photomasks registered thereto are in the exposureposition, the exposure unit is activated to direct actinic radiationtoward each surface of the board B through the photomask 58 laminated toeach surface thereof. While the exposure occurred, the board transferarrangement 46 is pivoted to the board-receiving position and thecarriages on the lifting and lowering arms are raised to occupy a heighttherealong corresponding to stored position.

After exposure is complete the board displacing arrangement lowers thenow-exposed board to the lamination position. The claim bar 208 and thelaminating rolls 302 and 304 are opened permitting the now-exposed boardto drop by gravity onto the carriages of the lowering arm. The carriageson the lowering arm are moved to the lower position while the boarddisplacing arrangement moves the backbar and clamp bar assembly to theregistration position in anticipation of the next board to be laminated.

The next successive unexposed board is conveyed by the conveyor to aposition intermediate the arms of the board transfer arrangement and theprocess is repeated. It is noted that the movement of the board transferarrangement from the board receiving to the board deposit positionserves to dispose the succeeding unexposed board into position below theregistration means and simultaneously deposit the exposed board onto asuitable carry-off conveyor.

We claim:
 1. A process of registering and imagewise exposing to actinicradiation a sequence of similar sheet substrates, each substratecontaining a photosensitive layer comprising the steps of:(1) advancinga substrate to a position in a device to undertake in either order orconcurrently(a) aligning the substrate and a photomask in apredetermined relationship to one another through a hinged relationshipof the photomask and the substrate to permit substantially identicalalignment of the photomask and each similar sheet substrate of thesequence; (b) applying a liquid between the photosensitive layer and thephotomask; (2) contacting through the liquid the substrate containingthe photosensitive layer and the photomask wherein liquid between thephotosensitive layer and the photomask is displaced when the substrateand photomask are brought into more intimate contact by an advancingpressure line whereby during said contacting substantially no movementof the photosensitive layer relative to the photomask occurs other thana more intimate contact due to displacement of the liquid in a liquidlayer and whereby at least one of a set of interfacial or viscous forcesdue to the liquid layer aids in holding the photosensitive layer andphotomask in a fixed position relative to one another; (3) exposing thephotosensitive layer to actinic radiation through the photomask; (4)removing the photomask from the exposed photosensitive layer; (5)removing the substrate whereby steps 1 to 5 can be repeated; and (6)repeating steps 1 to 5 for each of said similar sheet substrates wherebysubstantially identical imaged substrates are obtained.
 2. The processof claim 1 whereby liquid between the photosensitive layer and thephotomask is displaced when the substrate and photomask are brought intomore intimate contact by an advancing nip.
 3. The process of claim 1wherein the application of liquid is carried out with the substratesurface held in a substantially vertical plane.
 4. The process of claim1 wherein steps 1 to 5 are with the substrate surface held in asubstantially horizontal plane.
 5. The process of claim 1 wherein thesheet substrate contains a photosensitive layer on opposite sidesthereof and steps 1 to 5 are with the substrate held in a substantiallyvertical plane.
 6. The process of claim 2 wherein steps 1 to 5 are withthe substrate in an upright position and the substrate and photomask arebrought into more intimate contact by an advancing nip.
 7. The processof claim 5 wherein both sides of the sheet substrate are exposed toactinic radiation.
 8. The process of claim 1 wherein the photosensitivelayer is smooth.
 9. The process of claim 1 wherein the photosensitivelayer overlays an irregular relief pattern in the substrate.
 10. Theprocess of claim 1 wherein the photosensitive layer is positive working.11. The process of claim 1 wherein the photosensitive layer is negativeworking.
 12. The process of claim 1 wherein the photosensitive layercontains photohardenable component.
 13. The process of claim 1 whereinthe photosensitive layer contains a photohardenable additionpolymerizable component.
 14. The process of claim 14 wherein thephotohardenable component is photocrosslinkable or photodimerizable. 15.The process of claim 1 wherein the photomask is flexible.
 16. Theprocess of claim 1 without a support or cover sheet present between thephotosensitive layer and the photomask.
 17. The process of claim 1wherein the photosensitive layer is separated from the liquid layer by asupport or cover sheet which allows actinic radiation to pass.
 18. Theprocess of claim 1 wherein the liquid comprises water.
 19. The processof claim 1 wherein excess liquid is applied to cause flushing of thephotomask or substrate.
 20. The process of claim 1 wherein excess liquidis applied to cause flushing of the photomask and substrate.
 21. Theprocess of claim 1 wherein liquid is applied to both sides of thephotomask.
 22. The process of claim 1 wherein the photomask contains arelease coating.
 23. The process of claim 1 wherein the substrate alongat least a portion of one edge makes registration contact with acarrier.
 24. The process of claim 1 wherein at least two contact pointson the substrate makes registration contact with a carrier.
 25. Theprocess of claim 1 wherein step (2) registration contact is made byprecise alignment of details contained on the substrate containing thephotosensitive layer or substrate carrier with details on the photomask.26. The process of claim 1 wherein in step (1) (b) an excess of liquidis provided compared to the amount used to separate the substratecontaining the photosensitive layer and the photomask in the subsequentoperation of step (2) and whereby in step (2) a cleaning action isachieved on both the photosensitive layer and photomask by the use ofexcess liquid.
 27. The process of claim 26 wherein in step (1) (b) anexcess of liquid is provided compared to the amount used to separate thesubstrate containing the photosensitive layer and the photomask in thesubsequent operation of step (2) and whereby in step (2) a cleaningaction is achieved on both the photosensitive layer and photomask by theuse of an excess of liquid.
 28. A method of registration and imagewiseexposing to actinic radiation a sheet substrate with the oppositesurfaces containing photosensitive layers comprising the steps of:(1)advancing a substrate in an upright position in a device to undertake ineither order of concurrently(a) aligning the substrate with a photomaskcomprising two flexible sheet portions through a hinged relationship ofthe photomask and the substrate whereby each of sheet portions faces anopposite surface of the substrate; (b) applying liquid on both sides ofthe substrate between the photosensitive layers and the flexible sheetportions of the photomask; (2) contacting through the liquid the surfaceof each of the two photosensitive layers and the flexible sheet portionsof the photomask whereby during said contacting substantially norelative movement of the photosensitive layers to the photomask occursother than a more intimate contact due to displacement of the liquid ina liquid layer from two interfaces whereby liquid is displaced by a nipmoving relative to the substrate when the substrate and flexible sheetportions are brought into more intimate contact and whereby at least oneof a set of interfacial or viscous forces from the liquid aids to holdthe photosensitive layers and flexible sheet portions in a fixedposition relative to one another; (3) either sequentially orsimultaneously exposing both photosensitive layers to actinic radiationthrough the flexible sheet portion; (4) removing the flexible sheetportions from the exposed photosensitive layers; (5) removing thesubstrate whereby steps 1 to 5 can be repeated.
 29. The process of claim28 wherein steps 1 to 5 are repeated for a sequence of similar sheetsubstrates.
 30. A process of contacting and imagewise exposing toactinic radiation a sequence of similar sheet substrates, each substratecontaining a photosensitive layer comprising the steps of:(1) forming aliquid layer between the substrate and photomask with the substrate andphotomask in a hinged relationship to one another; (2) contacting thephotomask to the substrate whereby during said contacting substantiallyno movement of the photosensitive layer relative to the photomask occurson the liquid layer other than a more intimate contact due todisplacement of liquid from the liquid layer due to application of anadvancing pressure line with additional liquid applied between thephotomask and substrate in advance of the pressure line during saidcontacting of the photomask and substrate, and whereby at least one ofinterfacial or viscous force due to the liquid layer aids to maintainthe photosensitive layer and photomask in a fixed relationship; (3)exposing the photosensitive layer to actinic radiation through thephotomask; (4) removing the photomask from the exposed photosensitivelayer or a support sheet thereon; (5) removing the substrate wherebysteps 1 to 5 can be repeated; and (6) repeating steps 1 to 5 of saidsimilar sheet substrates whereby substantially identical imagedsubstrates are obtained.
 31. The process of claim 30 wherein(i) theadvancing pressure line begins at or near the edge of the photomaskwhich is in a hinge relationship with the substrate to form a hingeline, and (ii) the advancing pressure line advances in a directionsubstantially perpendicular to the hinge line and substantially parallelto the substrate surface.